Alternating current exciter lamp for sound reproducers



May 9, 1944. HAYNES 2,348,296

ALTERNATING CURRENT EXCITER LAMP FOR SOUND REPRODUCERS v Filed July 51, 1942 2 Sheets-Sheet 1 Sly/F725? sa 4X rmvsmwm musmwze 3nnento1:

May 1944- R. HAYNIEVS 2,348,296

ALTERNATING CURRENT EXCI'IER LAMP FOR SOUND REPRODUCERS Filed July 51, 1942 2 SheetsShet 2 3n'nentor i Robert L.Ha, yneg (Ittomeg Patented May 9, 1944 ALTERNA'TlNG' CURRENT EXCITER LAMP FOR SOUND REPRODUCERS 7 Robert L. Haynes, Indianapolis, Ind., assignor to Radio Corporation Delaware of America, a corporation of Application July 31,1942, Serial No. 452,987 A 9 Claims. (01. 250-415) This invention relates to an exciter lamp for providing the illumination for scanning sound track in a photoelectric, sound reproducer. It relates more particularly to a type of exciterlamp adapted to be operated by alternating current or to a combination of exciter lamps adapted to be so operated and to produce a minimum of hum in the reproduced sound.

The invention involves the use of one incandescent filament of fairly large diameter adapted to provide the larger portion of the scanning light, in conjunction with a second filament of much smaller diameter and thermal capacity supplied with current in such relation to the current in the main filament that the hum produced by the-smaller filament will neutralize that produced by the larger filament. I

One object of the invention is to provide a light source for sound reproducers which may be operated on alternating current with a minimum of hum in the reproduced sound.

Another object of the invention is to provide an A. C. exciter lamp which will produce a minimum of hum in the photocell current.

Another object ottheinvention is to supply an exciter lamp with an auxiliary light-source of less brilliance and higher percentage of hum for neutralizing thehum which'would be produced by the main exciterlamp. v

Other and incidental objects of the; invention will be apparent to those skilled in theart from a reading of the following specification; and an inspection of the accompanying drawings, in h. V I

Figure 1 is a diagrammatic illustration of one form of the invention;

Figure 2 is a section ofFig.1; H I,

Figure 3 is a diagrammaticelevation of a second form of the invention;

Figure 4 is a view of the filaments of the lamp shown in Fig. 3 as viewed from the right-hand side; and

Figure 5 is a schematic wiring diagram of a circuit which may be used in conjunction with the lamp shown in Figs. 3 and 4 or with the lamps shown in Figs. 1 and 2.

Inthe form of the invention shown in Figs. 1 and 2, the main or usual exciter lamp is shown at I0. The relatively heavy filament I I of this lamp provides light which strikes the entrance lens I3 of a sound reproducing optical system. The lamp I0 may be of any customary type as, for example, the -volt, 7 -ampere type. Since the lamp I0 is of relatively low voltage it is protakenon the line II-II vided with current from an ordinary A. C. source of supply through the transformer I2. A second lamp I6 is provided which has a filament I! much smaller'than that provided at vII in the main exciter lamp. This filament, for example, might operate at 8 volts and two amperes. This lamp I6 is provided with current through an appropriate transformer l5 fed through a phase shifter I4 which serves to shift the phase of the that supplied to the filament] I. V. r

The filament I! may be imaged on the filament II by an appropriate lens, such as I8, and the relative illumination supplied by the filament I"! may be controlled byan'appropriate iris diaphragm or analogous adjustable stop diagrammatically illustrated at It). v

The radiating surface of a given length of filament varies directly as the diameter of the wire while the thermal capacity of the filament varies as the square of the diameter of the wire. For this reason, the variations in temperature of the filament I! will be considerably greater than the variations in temperature of the filament I I. The filament I"! may therefore supply a relatively small proportion of the illumination and at the same time it will be capable of supplying light intensity fluctuations in opposite phase to' those produced by the filament II and of sufiicient amplitude toefiectivelyneutralize the intensity fluctuations produced by the'filament ll.

I am aware that it has previously been proposed to provide lamps with polyphase filaments of similar size but such arrangements have been impractical for the reasonthat it has been difficult to derive polyphase current from singlephase current, and phase shifting devices for accomplishing this result in conjunction with exciter lamps have been undulyexpensive and difflcult to adjust dueparticularly to the large cur rents and low voltages involved In the I present arrangement the disadvantages of the prior art devices have been avoided since the current which is shifted in phase is only a relatively small fraction of the total illuminating current.

Referring now to the form of the invention shown in Figs. 3 and 4: The filament 2| in the lamp. 20 corresponds to the filament II in Fig. 1 and is relatively heavy. The image of this filament is focused by the lens I3 on the objective lens 24 of the reproducing optical system and the image of the slit 23 is focused by the objective 24 upon the film F, the light passing through the film reaching the reproducing photocell 25. The filament corresponding to the filament I1 in Fig.

current supplied to the filament I1 relative to of Fig. 3 is shown in Fig. 5. The usual 110 volt,

60 cycle alternating current is supplied to the transformer which steps it down to an appropriate value. Current is supplied to the main filament 2| through the usual variable resistor 3| by which the current may be adjusted to the proper value. The current to the filament 22 is supplied through an appropriate phase'shifting network which includes the variable resistor in series with the filament 22 for; adjusting the current through this filament, the reactor 32 and resistor 33in series connected across the output of the transformer 30 andthe adjustable reactor 34 connected in series with the resistor 35 and the filament 22. The value of these reactors and resistors should be so adjusted that the current through the filament 22 is substantially 90 degrees out. of phase with the current through the filament 2|. Since the 60 cycle current through these filaments produces 120 cycle hum frequency,

this 90 degree phase shift will produce a 180 degree phaseshift in the variation in brilliance of the filament 22 relative to the filament 2| and these variations in illumination will tend to cancel, producing a minimumof hum.

Inasmuch as the filament 2|; s greater in diameter than the filament 22, the variations in temperature will tend to lag farther behind the current'in the case of the filament 2 Inasmuch as these variations cannot be accurately predicted, the reactor 34 is preferably made adjustable, so thatthe phase relation ofthe variations in illuminationof the two filaments may be-balancedto the best advantage.

Although the circuit shown in Figi 5 produces a lag in the phase of the smaller filament in rela-' tion to that of the larger, it will, be understood from Fig. 1 thatany known type of phase shifting circuit may be used and the phase relation of the smaller filament may be advanced theproper amount in relation to" that of the larger filament in order tosecure minimum hum. qI claim as my invention;

1. In a photoelectric apparatus, light producing means comprising. a main incandescent filament, a secondary filament of smaller diameter than the main filament and means for supplying alternating current in different phase relation to said filaments.-

2; In a photoelectric apparatus, light producing means comprising a main incandescent filament, a secondary filament of smaller diameter than the main filament and means for supplying alternating current in different phase relation to said filaments from a single phase source.

3. In a photoelectric apparatus, an exciter lamp comprising a main incandescent filament and a secondary filament of smaller diameter than the main filament, and means for supplying alternating current in different phase relation to said filaments.

4. In a photoelectric apparatus, light producing means comprising a main incandescent filament,

a secondary filament of smaller diameter than V the main filament and means for supplying alternating current in different phase relation to said filaments, from a single phase source and including means for shifting the phase relation of the current in the smaller filament relative to that in the main, filament. v

5. In a photoelectric apparatus, an exciter lamp comprising a main incandescent filament and a secondary filament of smaller diameter than the main filament and means for supplying-alternating current in different phase relation to said filaments from a single phase source.

6. In a photoelectric apparatus, light producing means comprising a main incandescent filament,-

a secondary filament of smallerdiameter than the main filament, means for supplying alternating current in different phase relation tosaid filaments, and means for superposi-ng the illumination from both of said filaments. V I

'7. In a photoelectric apparatus including -a photocell, light producing means com-prisinga main incandescent filament, a secondary filament of smaller diameter than the main filament, means for supplying alternating current in different phase relation to said filaments, means for imaging one-filament on the other filament, and means for directing light from both filaments to the photocell.

8. In a photoelectric apparatus, light producing means comprising a main incandescent filament,

' a secondary filament of smaller diameter than the mainfilament, means for supplying alternatingcurrentsfrom a single phase source in different phase relation to said filaments, and means for superposing theillumination from both of said filaments;

9. In a photoelectric apparatus, including a photocell light producing means comprising a main incandescent filament, a secondary filament of smaller diameter than the main filament, means for supplying alternating current from a single phase source in different phase relation to said filaments, means for-imaging one filament on the other filament, and means fordirecting light from both filaments to-the photocell.

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